Magnesium and its alloys, as the lightest structural materials, are widely applied to the fields of electronics, aerospace and automobile due to their desirable properties including high specific strength and specific stiffness, excellent conductivity of electricity and heat, easy to cut and recycle, and good damping characteristic. However, magnesium is a very active metal. Magnesium alloys parts need to be protected from corroding in the practical applications. A low cost and corrosion resistant treatment for magnesium alloys is chromate conversion film. Although chromate conversion film can provide good corrosion protection to magnesium alloys, the toxic hexavalent chromium ions have a bad effect on the environment. Thus, a chromate-free and high corrosion resistance conversion film is required to meet the urgent demands for magnesium alloys.